1. Field of the Invention
The present invention relates to a method and apparatus for creating an analysis model, and in particular, to a method and apparatus for creating analysis model data suitable for structural or fluid analysis. The present invention also relates to a program for creating an analysis model or a storage medium in which this program is recorded.
2. Description of the Prior Art
Conventionally, to create a three-dimensional shape model, elements from three-dimensional CAD data are generally divided to create an analysis model. With a complicated model, the number of steps required to form a model is huge and these steps require advanced techniques. A method utilizing voxels (volume pixels) has been proposed as one for automatically creating a solid model (hexahedron model). Voxel data define a three-dimensional model with a set of cubes utilizing three-dimensional rectangular coordinates, and the “voxels” are a concept corresponding to pixels in two dimensions. It is easy to completely automatically create FEM elements (analysis model data) from a three-dimensional model.
In this conventional example, however, since the voxel data are based on the rectangular coordinates, a very large number of divisions are required to accurately represent shape data, resulting in a huge number of elements. When, for example, a cube of 100 mm side is divided using 1-mm voxels, one million elements result. On the other hand, when the size of one element of the voxel is increased, the analysis accuracy decreases in calculations for deformation under loads and maximum stress in a location where stress is concentrated.
For example, Toshikazu TORIGAMI et al., “Automatic Generation of a Numerical Analysis Model Using a Voxel Model, and Its Application to Structural Analysis and Phase Shape Optimal Design”, Collection of Lecture Theses (I) Presented at the 74-th General Meeting of the Japan Machinery Society discloses that 64,333,160 voxel models are created for a mission case of a vehicle and that 7,063,070 nodes result. This conventional example states that a special analysis solver was also developed probably because the number of elements exceeded that which can be analyzed by normal analysis solvers and that when a super computer was used to provide a load transmitted from a bearing to a shaft and determine the distribution of this load, the analysis required about 18 hours.
If the results of the structural or fluid analysis of a mission case or a cylinder block that has a complicated shape are to be utilized to determine an optimal shape for reducing the weight of the cylinder block or the like while maintaining its required rigidity, the above-described example requires a special analysis solver and a large amount of time for calculations, thereby requiring high costs for simulations.